HDU 5672 String（尺取法）

Problem Description

There is a string  S. S only contain lower case English character. (10≤length(S)≤1,000,000)
How many substrings there are that contain at least  k(1≤k≤26) distinct characters?

 

Input

There are multiple test cases. The first line of input contains an integer  T(1≤T≤10) indicating the number of test cases. For each test case:

The first line contains string  S.
The second line contains a integer  k(1≤k≤26).

 

Output

For each test case, output the number of substrings that contain at least  k dictinct characters.

 

Sample Input

2 abcabcabca 4 abcabcabcabc 3

 

Sample Output

0 55

 

Source

BestCoder Round #81 (div.2)

 

题意:给你一个字符串，问你有多少子串包含k个不同的字母。

思路：如果有一段字符刚刚好满足条件，那么后面的包含这个串的子串全部满足，我们可以尺取l和r，对于一个r满足的话，后面len  -  r + 1个子串也满足，然后更新l就可以了，因为l和r是分开更新的，所以复杂度是O(n)。

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